The manufacturing of the pipes mentioned at the beginning is done in such a way that the inner duct is positioned into the outer duct by means of plastic spacing elements which are left in the finished pipe. Thereby, the arrangement of the spacing elements is complex and they form unwanted heat bridges or cold bridges respectively inside of the finished pipe. Additionally, the positioning of the inner duct is exact only at the spacing elements. Before the foaming, the inner duct can sag more or less between the spacing elements, this being only avoidable by a higher number of spacing elements. The foaming of the hollow space is done by means of a long foaming spear which is inserted into the hollow space between the inner and the outer duct from a first end and pushed forward until the closed second end. Subsequently, the foaming insulation material is brought in by means of the spear, wherein the spear is pulled back towards the first end, until the entire hollow space is filled with isolating foam in an as much as possible uniformly distributed way. The spacing elements are thereby formed and arranged in such a way that they don't interfere with the spear as much as possible; however, the insertion of the insulation is still complicated by the spacing elements. A device for tensioning a long spine is known from GB 344 356. The device is supposed to provide help during the manufacturing of flexible pipes by counteracting the sagging of the spine due to its own weight. From the international patent application WO 00/47387 a method and a device for the discontinuous manufacturing of heat-insulated pipes with an outer duct and an inner duct are known. Both ducts are aligned and centered prior to the foaming of the hollow space. In case of the inner duct, the aligning is done by applying a bending moment, being supposed to compensate the present sagging by the movement of the aligning and fixing elements. Optionally, a spacing element is used, which shall also make possible that both ducts are liftable from the outside.